AT&T MERLIN LEGEND System Reference Manual page 187

Features
Speed Dial
System Access
Toll Type
System Programmming
2-138 Disallowed Lists
A user with an unrestricted telephone cannot dial an outside number by via
Personal Speed Dial or System Speed Dial if the number is in a Disallowed List
assigned to the telephone, unless the number is dialed by using a marked
System Speed Dial code. If the number is dialed by using a marked System
Speed Dial code and the number includes a toll telephone number in addition to
an access number, dialing the number overrides any Disallowed List
assignment and a the telephone user can dial the number via a System Speed
Dial code.
In the Hybrid/PBX mode, a System Access button (include Shared System
Access buttons) cannot be used to dial an outside number when the number is
on a Disallowed List assigned to the telephone used to make the call.
When lines/trunks with different toll types are connected (for example, basic
lines/trunks and PRI facilities), a toll prefix (0 or 1) must be dialed for toll calls on
some lines/trunks and atoll prefix is not required for toll calls on other
lines/trunks. In this case, two Disallowed List entries are required to restrict
users from dialing specific area codes and/or telephone numbers. For example,
to restrict users from dialing calls in the 505 area code on both toll types, one
entry must be "1505" and the other entry must be "505." When the Disallowed
List is assigned to a station, the "1505" entry restricts users from making calls to
the 505 area code on lines/trunks that require a toll prefix and the "505" entry
restricts users from making calls (including local calls) to the 505 area code on
lines/trunks that do not require a toll prefix.
Establish, change, or remove Disallowed Lists.
Tables -> Disallow
Assign or remove Disallowed Lists from individual telephones.
Tables -> DisallowTo
Assign or remove Diallowed Lists from non-tie lines/trunks.
LinesTrunks -> RemoteAccss -> Non-TIE -> DisallowLst